Method for measuring the volume of solid bodies and a measuring and/or reference chamber for performing said method

ABSTRACT

Determination of the volume of solid bodies by plethysmometry: the bodies, such as human beings or animals, are brought into a measuring chamber (1) the volume of which is changed by means of a piston (8) within a cylinder (7). The change in pressure within the chamber (1) is measured and constitutes a measure of the volume of the body to be determined. The measurement may be performed with the aid of a reference chamber (5) in which the volume is also changed, i.e. by simultaneous movement of a piston (11) within a cylinder (10) together with piston (8) within cylinder (7). By comparison of pressures (by means of 17) between the chambers (1 and 5) a more accurate volume measurement is obtained than without reference chamber (5). The invention is based on the recognition that a quick change in volume is conducive also to a change in temperature and that living beings to be measured give off water vapor and heat, thus causing the measurement to be less accurate, and that this problem may be solved by filling the measuring chamber (1) and preferably also the reference chamber (5) for the major part thereof with a solid filler material (2, 6) having a plurality of interconnected cavities.

The invention relates to a method for measuring the volume of solidbodies and to a measuring and/or reference chamber for performing saidmethod.

It is often desired to determine the volume of human beings and animalse.g. for medical control purposes, for determining metabolic effects offood, for determining the merchandise value of animals, etc. in whichoften the weight should also be determined in order to calculate thespecific density on the basis of both said data.

In a known method for determining the volume of bodies there isperformed a weighing both in air and under water. With respect to theweighing under water this method is difficult to perform or evencompletely objectionable in case of e.g. old people, children, patientsand many animals.

Accordingly it has been attempted to provide a measurement of the volumeof solid bodies that may be carried out more easily by performing themeasurement by plethysmometry, i.e. by inserting the body to be measuredin a chamber in which the body to be measured is accomodated excludingthe chamber from the surroundings, changing the volume of said chamberto a predetermined known extent and measuring the change in pressurecaused by said change in volume.

The advantages thereof are that the measurement may be performed bymeans of a simple apparatus and that in case of human beings and animalsthe volume of the lungs and other corporal cavities filled with gas arenot included in the measurement in as far these cavities are in a moreor less free pressure equalizing connection with the exterior of thebody. Furthermore the method may well be applied for old people,patients, children and all kinds of animals without any objection.

In plethysmometry there is however the drawback that a relatively quickchange in volume not only induces a change in pressure but causes also achange in temperature to an extent not known accurately whereas in caseof human beings and animals the object to be measured gives off watervapour and heat causing the measurement to be even less accurate. Inorder to avoid this drawback as much as is possible one may perform thecompression very slowly, while also in case of a quickly performedcompression there may be a restoration of the initial temperature sothat the pressure will then yield a more proper picture of the volume inview of the isothermal compression thus simulated indirectly, but thelonger retention time then required will be uncomfortable for manyliving beings and will reduce the capacity of the measuring apparatuswhereas the heat and water vapour given off will affect more stronglythe result of the measurement and even slight leakages from themeasuring chamber will have a stronger effect than in case of a shortretention time.

The object of the invention is therefore to provide an improvement ofsaid method and more in particular such an improvement that even at ashort retention time an accurate measurement of the volume willnevertheless be possible by measuring a change in pressure caused by achange in volume.

According to the invention this object is preferably attained by amethod characterized in that the measurement is performed in a chamberlike indicated in which apart from the body to be measured at least amajor part is filled with a solid filler material having a plurality ofinterconnected cavities.

It has been found that the compression will occur thereby almost purelyisothermally so that a short retention time of e.g. 10 seconds willsuffice. Apparently the solid filler material absorbs the heat generatedby the compression sufficiently within a normal measuring range due tothe very large total surface in the cavities thereof while the fillermaterial shields the body to be measured from the major part of thecontents of the chamber such that the emission of heat and water vapourby said body do not affect the measurement unfavourably to a noticeableextent.

For achieving a still higher accuracy the measurement may be performedin a way known in principle by measuring the pressure differential uponsimultaneously quickly changing the volume of both the measuring chamberand of a reference chamber to a proportionate extent. The invention nowalso relates to such a system that in accordance with a preferredembodiment of the invention may be improved further by filling thevolume of the reference chamber for at least a major part thereof withsuch a material having a plurality of interconnected cavities. On thebasis of the pressure differential between the chambers the volume ofthe body in the measuring chamber may then be determined while thecompression within the reference chamber will occur also isothermallybecause the reference chamber has also been filled with a fillermaterial.

A measuring chamber for performing the above indicated method comprisingmeans for taking up bodies to be measured in said chamber, means forclosing said chamber, means for measuring the pressure within saidchamber and means for changing the volume of said chamber in a quick andcontrolled manner to a known extent is in accordance with the inventioncharacterized in that said chamber is filled at least for a major partthereof with a solid material having a plurality of interconnectedcavities; the same applying to an optionally used reference chamber.

Furthermore it is preferred that within the measuring chamber the solidfiller material is embodied such that said filler material isagglomerated into one or more solid filling bodies in which a recess isprovided for said solid body the volume of which is to be measured, saidrecess being in a shape adapted broadly to the shape of said body.

Preferably the filler material is elastic. Consequently the recess forthe body to be measured may be made such that in case of all bodies tobe measured or a large number thereof these bodies will be enclosed bysaid filler material while exerting some pressure on the bodies.Nevertheless some room may be left in the filler material e.g. at theside of the face of human beings and animals.

The invention will now be elucidated further in detail with reference tothe annexed drawing diagrammatically showing a measuring apparatusaccording to the invention.

Within a measuring chamber 1 there has been provided a fillingconsisting of elastic foamed polyurethane having a sponge structure,that is having intercommunicating pores. Said filling has been mountedin the form of a number of blocks 2 leaving a free space 3 in which thebody to be measured may be inserted. The chamber possesses an accessdoor that may be closed hermetically. Between said door and the body tobe measured there may be provided some easily removable blocks of thefiller material. The wall of the chamber may be transparent or may beprovided with one or more windows. For the measurement of the volume ofhuman beings there has been diagrammatically shown a free space 3 forthe upright position, which position may however also be a seatedposition or recumbent position. The interior cavities of the body takingpart in the compression are diagrammatically represented by a lungcavity 4. At the sides coinciding with the free space 3 the blocks 2will of course usually not possess flat boundary surfaces like indicatedin the drawing when human beings or animals have to be measured unlessthe filler material chosen possesses so high an elasticity that even insuch a case an almost complete enclosure of the body to be measured isachieved without causing an objectionable indentation pressure.

A reference chamber 5 has been filled with the same filler material inthe form of blocks 6.

Each one of the chambers 1 and 5 communicates with a cylinder includinga piston for the compression of the contents thereof. At 13 the chamber1 is in open communication with a cylinder 7 in which there has beeninserted a piston 8 mounted on a pistonrod 9, whereas at 14 the chamber5 is in open communication with a cylinder 10 including a piston 11mounted on the same pistonrod 9, said pistonrod running through apacking gland 12. At 15 the cylinder 7 is open whereas the cylinder 10possesses an opening at 16.

Between the chambers 1 and 5 there has been indicated diagrammatically apressure differential gauge at 17.

In order to keep the air in the chambers 1 and 5, respectively,everywhere constantly under the same uniformly equilibrated pressureupon compression by means of the pistons 8 and 11 and if such may bedesired in view of the blocks 2 and 6, the blocks may be provided withthe channels 18 connected in such a manner that they constitute a directconnection to the openings at 13 and 14. Usually this will however notbe necessary because of the porosity of said blocks as well asoptionally because of the rapid pressure equilibration through narrowgaps at the boundary surfaces of said blocks.

Upon insertion of a body to be measured within the free space 3 of thechamber 1 the pistonrod 9 is moved to the left over a fixed downdistance whereby the piston 8 decreases the volume of that part of thecylinder 7, communicating with the chamber 1 and increases the pressurewithin the chamber 1. Simultaneously the piston 11 increases thepressure within the reference chamber 5. The diameters of the pistons 8and 11 have been chosen such that upon a same stroke of the pistonrod 9the pistons 8 and 11 will displace a volume directly proportional withthe free volume of the chambers 1 and 5, respectively, that is to saythe volume thereof minus the volume of the filler material.

The said volume of the filler material may easily be determined byoperating the pistonrod 9 for increasing the pressure within thechambers 1 and 5 without the body to be measured being present in thefree space 3. By measuring the absolute pressure in each one of thechambers 1 and 5, for example by alternately disconnecting the pressuregauge from chamber 1 when performing the measurement in the chamber 5and from chamber 5 when performing the measurement in chamber 1 it ispossible to determine the effective free volume of each one of saidchambers.

It may easily be deduced that upon isothermal compression the volume ofthe body to be measured is determined by the e.g. thus found freeinitial volume of the chamber 1 including the volume of the joint 13 andthe cylinder space 7 to the left of the piston 8, the initial pressurein the two chambers 1 and 5, the change in volume in the cylinder 7caused by the piston 8 and the pressure differential measured at 17 uponcompression.

When measuring the volume of human beings the free volume of chamber 11is e.g. about 600 liters, of chamber 5 e.g. about 52 liters and thechange in volume of the cylinder 7 e.g. about 2.9 liters. The rate inwhich the pistonrod 9 is moved corresponds e.g. to a pressure increaserate of 50 mm head of water per second but may be chosen to be higherwithout any objection e.g. corresponding to a pressure increase rate of200 mm head of water per second. The human body can normally stand muchquicker pressure increases very well.

Preferably the pressure gauge 17 is in the form of a self-recordingpressure meter.

The fillermaterial does not have to meet stringent requirements withrespect to chemical and physical properties thereof. The polyurethanefoam having a sponge structure used in performing the tests had adensity of 15 kg/m³ and was supplied by Recticel, Kesteren, TheNetherlands. The linear cross section of the pores amounted to about 1mm. The elasticity was so high that the material could easily becompressed elastically to at least 50% of the initial volume whileelasticities up to 80-90% elastic compressibility may easily be achievedalthough such elasticities are usually not required. A honeycombconstruction of aluminium strip material may e.g. also be used, thechambers therein all communicating with each other and having lineardimensions of probably preferably at most 8 mm, preferably 5-6 mm. Thefiller material may e.g. also be wool or cotton or consist of metalstrip material and the like having a large total surface.

I claim:
 1. Method for measuring the volume of solid bodies byplethysmometry, i.e. by measuring the change in pressure caused bychanging the volume to a predetermined known extent of a chamber inwhich the bodies to be measured are taken up, and which is closed fromthe surroundings, characterized in that, apart from the body to bemeasured the space within the chamber is filled for at least a majorpart thereof with a solid filler material having a plurality ofinterconnected cavities.
 2. Method according to claim 1, in which themeasurement is performed by measuring the pressure differential uponsimultaneously quickly changing the volume of both the measuring chamberand of a reference chamber proportionally, characterized in that, thevolume of the reference chamber is filled for at least a major partthereof with a filler material having a plurality of interconnectedcavities.
 3. Measuring apparatus for measuring the volume of a solidbody by measuring the change in pressure resulting from changing thevolume of a chamber containing the body by a predetermined amount, saidapparatus comprising:a measuring chamber for receiving a body to bemeasured, the chamber having an opening for positioning the body in thechamber, the opening being closable so that the interior of the chamberis isolated from the ambient environment; a solid material having aplurality of interconnected cavities disposed in the interior of thechamber and filling a large part thereof; means for changing the volumeof a space including the interior of said chamber by a predeterminedamount; and means for measuring the change in pressure resulting fromthe change in volume, the change in pressure being representative of thevolume of the body being measured.
 4. Measuring apparatus according toclaim 6, wherein a recess is provided in the solid material forreceiving the body to be measured, said recess having a shape roughlycorresponding to the shape of the body being measured.
 5. Measuringapparatus according to claim 3 or 4, wherein the solid material isagglomerated into a plurality of blocks.
 6. Measuring apparatusaccording to claim 3 or 4, wherein said filler material is elastic. 7.Measuring apparatus according to claim 5, wherein interconnectedchannels are formed in said blocks for rapidly equilibrating pressure insaid chamber.
 8. Measuring apparatus according to claim 3 or 4, furthercomprising a reference chamber, and wherein said means for changing thevolume is positioned so as to simultaneously change the volume of thespace including the interior of the measuring chamber and to change by aproportional amount the volume of a second space including the interiorof the reference chamber, said means for measuring the change inpressure measuring the pressure differential between said measuringchamber and said reference chamber resulting from the changes of volume.9. Measuring apparatus according to claim 8, further comprising solidfiller material having interconnected compartments located in theinterior of said reference chamber.